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| United States Patent |
5,323,118
|
|
Tonogai
, et al.
|
June 21, 1994
|
Hinged displacement sensor
Abstract
This invention comprises two electrode plates 1a and 1c which are arranged
in parallel to each other, and a middle electrode plate 1b. One end of an
electrostatic capacity member 2 serves as a fixed portion 3 while the
other end thereof serves as a movable portion 4, and both end portions of
each of these electrode plates 1,1 are provided with hinges so that the
movable portion 4 is movable in parallel relative to the fixed portion 3.
Additive capacity is further provided by the insulating plate 6 to improve
the linearity of the detection output.
| Inventors:
|
Tonogai; Yoshihide (Tokyo, JP);
Takagi; Masaaki (Tokyo, JP)
|
| Assignee:
|
Copal Company, Limited (Tokyo)
|
| Appl. No.:
|
974160 |
| Filed:
|
November 10, 1992 |
Foreign Application Priority Data
| Nov 12, 1991[JP] | 3-296059 |
| Dec 27, 1991[JP] | 3-347497 |
| Current U.S. Class: |
324/661; 324/660; 361/280; 361/283.2 |
| Intern'l Class: |
G01R 027/26 |
| Field of Search: |
324/658,660,661,662
361/280
|
References Cited
U.S. Patent Documents
| 2968952 | Jan., 1961 | Stalder | 324/661.
|
| 4310806 | Jan., 1982 | Ogasawara | 324/661.
|
| 4439725 | Mar., 1984 | Ogasawara | 324/662.
|
| 5028875 | Jul., 1991 | Peters | 324/660.
|
| 5136286 | Aug., 1992 | Veneruso | 324/660.
|
Primary Examiner: Snow; Walter E.
Assistant Examiner: Brown; Glenn W.
Attorney, Agent or Firm: Hickman & Beyer
Claims
We claim:
1. A displacement sensor including a pair of facing pivotable electrode
members arranged such that overlapping opposing surfaces of said electrode
members define a confronting surface area, dielectric means which is
provided between said pair of electrode members, and a signal source for
applying an alternating voltage signal to a first one of said pair of
electrode members,
said displacement sensor arranged to be secured to an object being measured
so that at least one of a distance between said pair of pivotable
electrode members and said confronting surface area is non-linearly varied
as a function of a displacement of said object being measured, such that a
potential of a second one of said pair of electrode members is indicative
of the displacement of said object being measured.
2. A displacement sensor including first and second pivotable electrode
members arranged so as to be facing each other, a third pivotable
electrode member disposed between said first and second electrode members
so as to be facing said first and second electrode members such that
opposite surfaces of said third electrode member overlap opposing surfaces
of said first and second electrode members to define a first and second
confronting surface area, dielectric means which is provided between said
first and third electrode members and between said second and third
electrode members, and a signal source for applying an alternating voltage
between said first and second electrode members,
said displacement sensor arranged to be secured to an object being measured
so that at least one of a distance between said first and third electrode
members and a distance between said second and third electrode members,
and said first and second confronting surface areas are non-linearly
varied as a function of a displacement of said object being measured, such
that an electric potential of said third electrode member is indicative of
the displacement of said object being measured.
3. A displacement sensor including:
spaced apart first and second electrode members;
a third electrode member disposed between said first and second electrode
members to face respective opposing surfaces of said first and second
electrode members to define first and second confronting surface areas;
dielectric means, a first portion of which is provided between said first
and third electrode members and a second portion of which is provided
between said second and third electrode members; and
a signal source for applying an alternating voltage between said first and
second electrode members,
wherein said displacement sensor is arranged to be secured to an object
being measured so that at least one of a distance between said first and
third electrode members and a distance between said second and third
electrode members and said first and second confronting surface areas is
non-linearly varied as a function of a displacement of said object being
measured, and a detection result of the displacement being output as an
electric potential of said third electrode member, wherein one end portion
of each of said electrode members is linked to the object being measured,
each one end portion having an associated first hinge which is movable in
a direction where the displacement to be measured is increased and
decreased, wherein associated first hinge positions of said first and
second electrode members are different from that of said third electrode
member.
4. The displacement sensor as claimed in claim 3, wherein said associated
first hinges and associated second hinges of a second end portion of each
of said electrode members are formed integrally with said electrode
members.
5. A displacement sensor including;
a plurality of electrode members arranged to face each other;
a movable member securing one end portion of each of said electrode members
and secured to an object being measured; and
a fixed member securing a second end portion of each of said electrode
members;
wherein at least one of a gap interval between middle portions of said
electrode members and a confronting surface area defined by overlapping
opposing surfaces of the electrode members is non-linearly varied as a
function of the displacement of the object being measured.
6. The displacement sensor as claimed in claim 5, further including
dielectric means which has a dielectric constant higher than the
dielectric constant of a material separating the confronting surfaces of
the electrode members, the dielectric means being provided between the
second end portions of said electrode members.
7. The displacement sensor as claimed in claim 5, further including
dielectric means which has a dielectric constant higher than the
dielectric constant of a material separating the confronting surfaces of
the electrode members, the dielectric means being provided between the one
end portions of said electrode members which are secured to said movable
member.
8. The displacement sensor as claimed in claim 5, wherein said electrode
members are formed of conductive plates which are arranged in parallel and
have the same characteristics, and the middle portions thereof are
capacitively linked to one another to form a parallel link mechanism.
9. The displacement sensor as claimed in claim 8, further including a
deadweight arranged to be secured to the movable portions of said
electrode members.
10. The displacement sensor as claimed in claim 5, wherein said electrode
members comprise three identical conductive plates which are arranged in
parallel, and wherein an intermediate portion of a middle conductive plate
of said three conductive plates is offset from intermediate portions of
the other conductive plates.
11. The displacement sensor as claimed in claim 10, wherein one end portion
of said conductive plate disposed at the middle position is connected to
an amplifier and a rectifier while the other conductive plates are
connected to an alternating power source to detect a direct current
indicative of said displacement through said rectifier.
12. A displacement sensor, including;
plural electrode members arranged to face one another;
a movable member securing one end portion of each of said electrode members
and arranged to be secured to an object being measured; and
a fixed member securing a second end portion of each of said electrode
members;
wherein at least one of a gap interval between associated middle portions
of said electrode members and a confronting surface area defined by
overlapping opposing surfaces of the electrode members is non-linearly
varied as a function of the displacement of the object being measured and
wherein the one end portions of said electrode members and said movable
member are linked, each one end portion having a first hinge which is
movable in a direction where the displacement to be measured is increased
and decreased, and wherein second end portions of said electrode members
and said fixed member are linked to each other, each second end portion
having a second hinge which is movable in a direction where the
displacement to be measured is increased and decreased.
13. The displacement sensor as claimed in claim 12, wherein said first and
second hinges comprise plural holes formed along the end portions of said
electrode members so as to be aligned in a line.
14. The displacement sensor as claimed in claim 12, wherein said first and
second hinges are formed in the form of bellows along the end portions of
said electrode members.
15. The displacement sensor as claimed in claim 12, wherein said first and
second hinges each have a thickness that is less than the thickness of the
associated middle portions.
16. The displacement sensor as claimed in claim 12, wherein said first and
second hinges comprise elongated holes formed along the end portions of
said electrode members.
17. A displacement sensor including:
a pair of facing pivotable electrode members arranged such that overlapping
opposing surfaces of said electrode members define a confronting surface
area;
dielectric means which has a dielectric constant higher than the dielectric
constant of a material separating the confronting surfaces of the
electrode members, and which is provided between fixed end portions of
said pair of electrode members; and
a signal source for applying an alternating voltage signal to a first one
of said pair of electrode members,
wherein said displacement sensor is arranged to be secured to an object
being measured so that at least one of a distance between said pair of
pivotable electrode members and said confronting surface area is
non-linearly varied as a function of a displacement of said object being
measured, such that a potential of a second one of said pair of electrode
members is indicative of the displacement of said object being measured.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a capacitance type displacement sensor which is
used to detect a displacement of an object, such as tilt angle,
acceleration, position etc., for example.
2. Related Background Art
Displacement gauges of the prior art include contact-type and non-contact
type devices.
The contact-type displacement gauge has a construction that a brush 61
secured to the tip of a pendulum 60 is slid in contact with a resistor 62
which is supplied with a constant voltage as shown in FIG. 1, and voltages
into which the constant voltage is divided by the brush 61 are output as a
detection output to detect a tilt angle.
On the other hand, as shown in FIG. 2, the non-contact type displacement
gauge has a construction that a magnet 71 secured to the tip of a pendulum
60 is swung along side magnetic resistant elements 72 and 73 without
contacting with the magnetic resistant elements 72, 73, and a tilt angle
is differentially detected on the basis of the variation in resistant
values of the magnetic resistant elements 72 and 73.
The contact-type displacement gauge as described above is a displacement
gauge in which a contact portion such as a brush is displaced along a
resistor while contacting the resistor to thereby output a voltage
obtained by split resistance, and it has a limited life time because it is
operated in a contact mode. A rotational torque is increased due to
friction of the contact portion, so that an output has large hysteresis.
Conversely, in order to reduce the hysteresis, a larger deadweight or a
longer arm is required, so that the displacement gauge becomes more
enormous and weighty. Therefore, the contact-type displacement gauge has
problems in its durability and detection accuracy for displacement amount.
In the non-contact type displacement gauge, the problem as described above
does not occur. However, the magnetic characteristic of the magnet is
liable to be deteriorated with time lapse, so that there are problems in
detection accuracy and durability. In addition, the magnetic resistant
element is formed of a semiconductor and thus its temperature
characteristic is degraded, so that an appropriate temperature
compensation must be considered for use over a broad temperature range.
SUMMARY OF THE INVENTION
This invention has been implemented in view of the above problems, and has
an object to provide a displacement gauge having high durability in which
no hysteresis occurs and no deterioration of the detection accuracy for
displacement amount occurs even for use over a long time and under a
relatively-broad temperature range.
In order to attain the above object, this invention is characterized by
including a pair of electrode members arranged so as to be confronted to
each other, additive capacity means having constant capacity which is
provided between the pair of electrode members and a signal source for
applying an alternating voltage to one of the pair of electrode members,
the displacement sensor being secured to an object being measured so that
at least one of a distance between the pair of electrode members and a
confront area thereof is non-linearly varied in accordance with a
displacement to be measured, and a detection result for the displacement
being output as an electric potential of the other of the pair of
electrode members.
Here, it is preferable that one end portion of each of the pair of
electrode members is linked to the object being measured through a first
hinge movable in a displacement direction to be measured, material having
dielectric constant higher than that of environmental material is
interposed between the other ends of the pair of electrode members to form
additive capacity means, and the constructive portion of the additive
capacity means is linked to middle portions of the pair of electrode
members.
This invention is also characterized by including first and second
electrode members arranged so as to be confronted to each other, a third
electrode member disposed between the first and second electrode members
so as to be confronted to the first and second electrode members, additive
capacity means having constant capacity which is provided between the
first and third electrode members and between said second and third
electrode members, and a signal source for applying an alternating voltage
between the first and second electrode members, the displacement sensor
being secured to an object being measured so that at least one of a
distance between the first and third electrode members and between the
second and third electrode members, and a confront area thereof is
non-linearly varied in accordance with a displacement to be measured, and
a detection result for the displacement being output as an electric
potential of the third electrode member.
In this case, it is preferable that one end portion of each of the first,
second and third electrode members is linked to the object being measured
through a first hinge movable in a displacement direction to be measured,
and the link position of the third electrode member and the first hinge is
different from those of the first and second electrode members and the
first hinge in the displacement direction.
It is also preferable that material having a dielectric constant higher
than that of environmental material is interposed between the other end
portions of the first, second and third electrode members to form additive
capacity means, and the constructive portion of the additive capacity
means is linked to a middle portion of each of the first, second and third
electrode members through a second hinge movable in the displacement
direction.
Through displacement to be measured, for example, the electrode members
which are arranged in parallel are inclined while keeping their parallel
state, and this inclination follows the variation of the distance between
the electrode members and the confront area thereof.
As a result, the electrostatic capacity between the electrode members is
varied, and thus by applying an alternating voltage to an electrode
member, the displacement amount can be detected on the basis of the
electric potential of the other electrode member. That is, by forming the
capacitance type sensor of three electrode members and positionally
deviating a hinge of the middle electrode member from hinges of the
electrode members at both sides of the middle electrode member in a
direction vertical to the displacement direction, through the inclination
of the electrode members due to the displacement, the confront distance
between the middle electrode member and the electrode member at one side
of the middle electrode member and the confront distance between the
middle electrode member and the electrode member at the other side of the
middle electrode member are in such a relationship that one distance is
decreased as the other distance is increased.
This is equivalent to a relationship that the electrostatic capacity
between the middle electrode member and the electrode member at one side
of the middle electrode member is increased as the electrostatic capacity
between the middle electrode member and the electrode member at the other
side of the middle electrode member is decreased, and vice versa.
Therefore, these variations can be differentially detected by connecting
the electrode members at both sides to an alternating power source and
obtaining a detection output from the middle electrode member, so that an
accurate detection output which has been subjected to temperature
compensation can be obtained. In this case, since the variation of the
electrostatic capacity is non-linear (for example, sinusoidal) with
respect to the displacement to be measured, a linear output voltage can be
detected by providing additive capacity.
The present invention will become more fully understood from the detailed
description given hereinbelow and the accompanying drawings which are
given by way of illustration only, and thus are not to be considered as
limiting the present invention.
Further scope of applicability of the present invention will become
apparent from the detailed description given hereinafter. However, it
should be understood that the detailed description and specific examples,
while indicating preferred embodiments of the invention, are given by way
of illustration only, since various changes and modifications within the
spirit and scope of the invention will become apparent to those skilled in
the art form this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the construction of a conventional contact-type
displacement gauge,
FIG. 2 is a diagram showing the construction of a conventional non-contact
type displacement gauge,
FIG. 3 is a side view of a displacement gauge of a first embodiment
according to this invention,
FIG. 4 is a perspective view of a displacement gauge of a second embodiment
according to this invention,
FIG. 5 is a cross-sectional view of the embodiment as shown in FIG. 4 when
the hinge is modified,
FIG. 6 is a circuit diagram of a detection circuit which is applicable to
the embodiments as shown in FIGS. 4 and 5,
FIG. 7 is a diagram of variation characteristic of a detection output,
FIG. 8A is a graph of actually-measured data, showing angle dependence of
detection output,
FIG. 8B is a graph of actually-measured data, showing linearity of
detection output,
FIG. 9A is a graph of actually-measured data, showing angle dependence of
detection output,
FIG. 9B is a graph of actually-measured data, showing linearity of
detection output,
FIGS. 10A to 10D are views showing modifications of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The displacement gauge of a first embodiment according to this invention
will be described with reference to FIG. 3. Two electrode plates 1,1
formed of conductive material are arranged in parallel to form an
electrostatic capacity member 2. Both of confronting end portions of the
respective electrode plates 1,1 are fixedly laminated with adhesive agent
or the like while an insulating plate 6 is interposed therebetween. One
end of the electrostatic capacity member 2 is used as a fixed portion 3
while the other end thereof is used as a movable portion 4, and hinges 5,
5 are provided to both end portions of each electrode plate 1 so that the
movable portion 4 is movable in parallel to the fixed portion 3. The
respective hinges 5 are provided so as to be in contact with the lower
surface of the fixed portion 3 and the upper surface of the movable
portion 4 respectively, and with this construction, a so-called parallel
link mechanism is formed for both electrodes 1,1.
In addition, electrode terminals 7,7 which are connected to the electrode
plates 1,1 are provided at the upper surface of the fixed portion 3, one
serving as a power-source terminal while the other serves as an output
terminal.
In the above construction, representing gap interval and effective
confronting area of the electrode plates 1,1 between the hinges 5,5 of
both end portions by L.sub.1 and S.sub.1, and representing gap interval
and effective confronting area of the electrode plates at the outside of
the hinges 5,5, that is, at the fixed portion 3 and the movable portion 4
of the electrostatic capacity member 2 by L.sub.0 and S.sub.0, the
electrostatic capacity C of the electrostatic capacity member 2 is
represented as follows:
C=.epsilon..sub.0 (S.sub.1 /L.sub.1 +.epsilon..sub.S .multidot.S.sub.0
/L.sub.0)
Here, .epsilon..sub.0 represents vacuum dielectric constant, and
.epsilon..sub.S represents dielectric constant of the insulating plate 6.
Here, if the movable portion 4 is displaced relatively to the fixed
portion 3 so that the electrode plates 1,1 are inclined by an angle .PHI.,
a gap interval L.sub.1 between the electrode plates after the displacement
is represented by L.sub.0 cos .PHI., and the electrostatic capacity is
varied with the angle .PHI. in accordance with the above equation.
Therefore, if the movable portion 4 is so designed as to be displaced
through a pin (not shown) or the like in accordance with the displacement
of an object being measured, the displacement of the object being measured
can be measured on the basis of the variation of the electrostatic
capacity C. In addition, if a deadweight 9 is secured to the movable
portion 4, a tilt angle of the fixed portion 3 with respect to the gravity
direction could be also measured. An additive floating capacity C.sub.0
=.epsilon..sub.0 .multidot..epsilon..sub.S .multidot.S.sub.0 /L.sub.0,
which is formed by interposing the insulating plate 6 of dielectric
constant .epsilon..sub.S, functions to improve the non-linearity of the
output voltage and provide a linear output. This function is remarkable
particularly in a second embodiment as described later.
As described above, the displacement gauge according to this embodiment has
an analog output, so that it will theoretically have an infinite
resolution, and it has an endless lifetime because it is operated in a
non-contact mode.
As described above, according to the displacement gauge of this embodiment,
since the displacement is detected on the basis of the variation in
electrostatic capacity which is caused by variation of the distance
between the electrodes due to the inclination of the electrode plates, no
hysteresis occurs and no deterioration in durability and detection
accuracy due to abrasion occurs. In addition, the displacement gauge of
this embodiment has no deterioration in detection accuracy with time
lapse, and is usable over a broad temperature range.
Upon action of an elastic force on the hinge, the electrode plate can be
inclined by an angle corresponding to a force acting on the movable
portion through acceleration. Therefore, the displacement gauge of this
embodiment is usable as an acceleration sensor.
A second embodiment in which this invention is applied to an inclinometer
will be hereunder described with reference to FIGS. 4 and 5.
In this embodiment, three electrode plates 1a, 1b and 1c are arranged
mutually in parallel to one another, and both ends of the respective
electrodes 1a, 1b and 1c are fixedly laminated through insulating plates 6
using adhesive agent in the same manner as the first embodiment as
described above, thereby forming an electrostatic capacity member 2
comprising substantially two condensers. The dielectric constant of
insulating plates 6 is higher than the dielectric constant of a material,
such as air, that separates the three electrode plates 1a, 1b, and 1c. The
electrostatic capacity member 2 is so designed that the upper end thereof
serves as a fixed portion 3 while the lower end thereof serves as a
movable portion.
In addition, as shown in FIG. 4, the fixed portion 3 is provided with a
bracket 8 through which the electrostatic capacity member 2 is pendently
secured to the object being measured, and a deadweight 9 is secured to the
movable portion 4.
Hinges 5 are provided to both end portions of each electrode plate so that
a parallel link mechanism for parallel displacing the movable portion 4
relatively to the fixed portion 3 is formed by the electrode plates 1a, 1b
and 1c. In this case, the hinge 5 of the second electrode plate 1b at the
middle position is located so as to be positionally deviated in a
up-and-down direction from the locating positions of the hinges 5 of the
first and third electrode plates 1a and 1c at the right and left sides by
a predetermined amount.
With this arrangement, a distance between the electrode plates 1a and 1b
and a distance between the electrode plates 1b and 1c are such that
through the inclination of the electrostatic capacity member, one distance
is increased as the other distance is decreased, and vice versa (see FIG.
5).
Each hinge 5 comprises a bend portion which is formed integrally with the
electrode plate 1a, 1b, 1c and which is elastic and bendable. The bend
portion may be formed by processing a part of the member so as to be
bendable like an elongated hole as shown in FIG. 4 or a thin-thickness
portion as shown in FIG. 5, or may be formed by a flexible member having
.OMEGA. or other shapes in section.
On the other hand, the fixed portion 3 is provided with electrode terminals
7a, 7b, 7c which are connected to the electrode plates 1a, 1b and 1c, and
as shown in FIG. 6, the electrode plates 1a and 1c at the right and left
sides are connected to an alternating power source 10. An alternating
output from the middle electrode plate 1b is amplified by an amplifier 11,
and then a detection output of direct-current level is obtained through a
rectifier 12.
In the construction as described above, if an object being measured is
inclined and upon action of the deadweight 9 the electrode plates 1a, 1b
and 1c are inclined by an angle .PHI. toward the right side as indicated
by an imaginary line of FIG. 5, due to the positional deviation h of the
hinge 5 of the middle electrode plate 1b, the distance L.sub.1 between the
middle electrode plate 1b and the electrode plate 1a at the left side is
represented:
L.sub.1 =(L.sub.0 -h.multidot.tan .PHI.) cos .PHI.
and the distance L.sub.2 between the middle electrode plate 1b and the
electrode plate 1c at the right side is represented:
L.sub.2 =(L.sub.0 +h.multidot.tan .PHI.) cos .PHI.
Since the positive and negative polarities of h.multidot.tan .PHI. are
reversed between the distance L.sub.1 between the middle electrode plate
1b and the electrode plate 1a at the left side and the distance L.sub.2
between the middle electrode plate 1b and the electrode plate 1c at the
right side, the electrostatic capacity between the electrode plates 1b and
1a and the electrostatic capacity between the electrode plates 1b and 1c
are differentially varied.
Therefore, affections due to variation in temperature and variation in
dielectric constant are offset, and the accurate detection output in
accordance with the tilt angle can be obtained.
When the hinge 5 is constructed by the elastic and bendable bend portion as
described above, the tilt angle .theta. of the object being measured is
not coincident with the inclination angle .PHI. of the electrode plates
1a, 1b and 1c due to an elastic force acting on the hinge 5, however, the
following equation is satisfied between .PHI. and .theta. where the spring
constant of the hinge 5, the distance between the hinges at both end
portions and the weight of the dead weight 9 are represented by K, L.sub.V
and M, and .theta. can be calculated from the detection output in
accordance with .PHI..
.PHI.=sin.sup.-1 (M/K.multidot.L.sub.V .multidot.sin .PHI.)
FIG. 7 shows the variation characteristic of the detection output with the
inclination angle .PHI. of the three electrode plates 1a, 1b and 1c. When
insulating electrostatic capacity (floating capacity) obtained at the
outside portions of the hinges 5, that is, the insulating plates 6 of the
fixed portion 3 and the movable portion 4 is not added to the
electrostatic capacity between the respective electrode plates, the
variation characteristic becomes a non-linear variation characteristic as
indicated by a line "A".
However, by adding a predetermined floating capacity to the electrostatic
capacity between the respective electrode plates which are located between
the hinges 5 at both end portions, the variation characteristic becomes a
substantially linear variation characteristic as indicated by a line "B".
Therefore, the output has high linearity with respect to the tilt angle,
and has high stability with respect to variation of temperature.
Further, the output is not a digital output, but a linear output, so that
the resolution is small. In addition, since it is an absolute output, even
when a power failure occurs during a measurement, there is no case where a
position after restoration is unclear.
FIGS. 8A to 9B show actually-measured values of the variation
characteristic. In both cases, the zero capacity excluding the additive
capacity serving as the floating capacity is equal to 42.5 pF. The
measurement was made as a tilt-angle sensor of .+-.65 degrees where the
spring coefficient of the hinge is set to 0.6 for the example of FIGS. 8A
and 8B, and 0.8 for the example of FIGS. 9A and 9B.
FIG. 8A shows angle (deg) dependence of an output; {C.sub.1 /(C.sub.1
+C.sub.2)}, and FIG. 8B shows its linearity [%FS].
Here, the linearity [%FS] can be calculated using the following equation
after a regression-line coordinate is calculated from angle-output data.
Linearity[%FS]={(actually-measured value of .theta.)-(coordinate value of
.theta. calculated from regressionline)}.times.100/{(maximum value of
output)-(minimum value of output)}
In the figures, a curved line "A" shows a case where the additive floating
capacity is 50 pF, a curved line "D" shows a case where there is no
additive floating capacity, and curved lines "E" and "F" show cases where
the additive floating capacities are 90 pF and 110 pF, respectively. It is
understandable that a non-linear variation can be approached to a linear
variation by adding the floating capacity.
The same matter as described above is satisfied for the example of FIGS. 9A
and 9B. A curved line "A" shows a case where the additive floating
capacity is 50 pF by using a polyimide film (.epsilon..sub.S =3.5), and a
curved line "B" shows a case where the floating capacity is 30 pF by using
a Teflon film (.epsilon..sub.S =2.2). A curved line "C" shows a case where
the floating capacity is assumed to be 15 pF, and a curved line "D" shows
a case where there is no additive floating capacity. In this case, it is
also understandable that the detection characteristic can be linear.
Since a capacity value must be generally increased to improve the detection
accuracy for capacity, the area of a condenser portion must be enlarged,
and a gap interval between the electrodes must be narrowed. In this
embodiment, a support portion of the electrode is fixed, and thus the
electrode is not rickety, so that the gap between the electrodes can be
easily narrowed and the displacement gauge can be miniaturized and
lightened. In addition, a differential output is obtained on the basis of
differentially-varying capacities, and thus the output is stable.
Since no obstacle is disposed in the moving direction of the movable
portion, the moving amount of the movable portion can be increased.
Further, both ends of the electrode are so designed to be fixed, so that
the gap interval between the electrodes can be decreased. As described
above, the displacement gauge of this embodiment performs an amplifying
mechanism for the variation in gap interval between the electrodes by
positionally deviating the electrodes, so that the capacity variation is
intensified for the capacity value, the accuracy is also improved and the
output is also stabilized.
Upon acting the elastic force on the hinge 5, the electrode plate can be
inclined by an angle corresponding to a force acting on the movable
portion through acceleration, so that the displacement gauge of this
invention can be used as an acceleration sensor. Further, by securing the
movable portion to an object which is moved relatively to the fixed
portion, this invention can be also used as a sensor for linear positional
displacement.
Next, modifications of this invention will be described with reference to
FIG. 10. A first modification as shown in FIG. 10A uses electrode plates
each having base portions which are secured to the fixed portion 3 and the
movable portion 4 and having smaller thickness. The thickness variation of
the electrode plates 1 is designed such that a smooth curve is
continuously varied, and the electrode plates 1 are formed of material
having strong resistance to creep. A second modification as shown in FIG.
10B uses electrode plates 1 each having semispherical grooves in the
neighborhood of the fixed portion 3 and the movable portion 4, so that the
portions having the semispherical grooves have smaller thicknesses. A
third modification as shown in FIG. 10C uses electrode plates 1 each
having multiple holes which are formed in the neighborhood of the fixed
portion 3 and the movable portion 4 in such a manner as to be aligned in a
line along the end portion of the fixed portion 3 and movable portion 4.
Therefore, each electrode plate 1 is easily bendable around an axis
corresponding to the alignment direction of the holes. A modification as
shown in FIG. 10D uses electrode plates 1 each having bellows formed in
the neighborhood of the fixed portion 3 and the movable portion 4. The
bellows are formed so as to be returnably bendable. Therefore, the gap
interval between the electrode plates in a return state is invariable.
As is apparent from the foregoing, according to this invention, through the
displacement to be measured, the parallel-arranged electrode members are
inclined while keeping their parallel state, and through this inclination
the electrostatic capacity between the electrode members is varied.
Therefore, by applying an alternating voltage to a certain electrode
member, the displacement amount can be detected on the basis of the
potential of the other electrode member. Further, if the electrostatic
capacity member is formed of three electrode members and the hinge of the
middle electrode member is positionally deviated from the hinges of the
electrode members at both sides of the middle electrode member in a
direction vertical to the displacement direction, through the inclination
of the electrode members due to the displacement, the electrostatic
capacity between the middle electrode member and the electrode member at
one side of the middle electrode member and the electrostatic capacity
between the middle electrode member and the electrode member at the other
side of the middle electrode member are increased and decreased
respectively, and vice versa.
Therefore, by connecting both of the electrode members to the alternating
power source and obtaining a detection output from the middle electrode
member, these variations can be differentially detected, and an accurate
detection output which has been subjected to the temperature compensation
can be obtained. In this case, the variation of the electrostatic capacity
is non-linear (for example, sinusoidal) with respect to the displacement
to be measured, so that a linear output voltage can be detected by
providing additive capacity.
The displacement can be detected on the basis of the variation of the
electrostatic capacity which is caused by the variation in the distance
between the electrode members and the confront area thereof, so that
unlike the contact-type displacement gauge no hysteresis occurs and no
deterioration in durability and detection accuracy due to abrasion occurs.
In addition, since this invention uses no magnet and no semiconductor such
as the magnetic resistant element unlike the conventional non-contact type
of displacement gauge, this invention has effects that the detection
accuracy is not deteriorated even with time lapse, and that the
displacement gauge can be used over a broad temperature range.
From the invention thus described, it will be obvious that the invention
may be varied in many ways. Such variations are not to be regarded as a
departure from the spirit and scope of the invention, and all such
modifications as would be obvious to one skilled in the art are intended
to be included within the scope of the following claims.
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